Optically pure amino acids are used as ligands for asymmetric catalysts, or may be widely utilized as starting materials or intermediates necessary to synthesize a variety of medical products and physiologically active materials, and are thus regarded as very important from the industrial point of view (Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336-345).
Amino acids are inexpensively and economically produced via fermentation. However, amino acids resulting from fermentation are limited to only the L-amino acids, for natural amino acids. Although optically pure D-amino acids and non-natural amino acids are produced via an enzyme process or an optical resolution process, they cost a lot to prepare and the prices thereof are therefore about 5˜10 times higher than those of natural L-amino acids resulting from fermentation, and mass production thereof is difficult to achieve (Maruoka, K.; Ooi, T. Chem. Rev. 2003, 103, 3013).
The present inventors have developed a method of transforming L-amino acid into D-amino acid based on chirality of chiral aminoalcohol and amino acid via an imine bond using a binaphthol derivative having an aldehyde group as represented by the following chemical formula ((a) Park, H.; Kim, K. M.; Lee, A.; Ham, S.; Nam, W.; Chin, J. J. Am. Chem. Soc. 2007, 129, 1518-1519; (b) Kim, K. M.; Park, H.; Kim, H.; Chin, J.; Nam, W. Org. Lett. 2005, 7, 3525-3527).
[Binaphthol Derivative]

The binaphthol derivative may enantioselectively react with amino acid to form an imine, and enables L-D optical transformation of amino acid in an organic solvent such as DMSO. As disclosed in previous patents and papers (Park, H.; Kim, K. M.; Lee, A.; Ham, S.; Nam, W.; Chin, J. J. Am. Chem. Soc. 2007, 129, 1518-1519), the L-D optical transformation method includes performing optical transformation in DMSO and then extracting the entire solution with water and an organic solvent. By this method, amino acid is transferred to a water layer and the binaphthol derivative is transferred to an organic layer, and the binaphthol derivative of the organic layer is recovered by removal of the organic solvent and can be re-used. In the case where the L-D optical transformation will be performed by means of the above method, a period of time required for optical transformation is about 24˜48 hours. Because the DMSO solvent is freely miscible with both the water and the organic solvent, it is impossible to recover DMSO. Furthermore, DMSO must be completely removed from the organic layer in order to recover the binaphthol derivative. For this purpose, a large amount of water has to be used, and the working volume is increased, which undesirably decreases productivity. Also, the case where another solvent that is immiscible with water is used in lieu of DMSO is problematic because the reaction time of L-D optical transformation is further increased.